Google rolled out its first targeted data update after the "Penguin" algorithm update. This confirmed that Penguin data was being processed outside of the main search index, much like Panda data.
1st Documented Update — September 2002
Before "Boston" (the first named update), there was a major shuffle in the Fall of 2002. The details are unclear, but this appeared to be more than the monthly Google Dance and PageRank update. As one webmaster said of Google: "they move the toilet mid stream".
Regular Google algorithm updates and how it might affect your website.